Image processing apparatus

ABSTRACT

An apparatus for processing a two-dimensional image obtained by scanning sensor arrays of image detectors perpendicular thereto, the apparatus including an image memory for storing pixel data output by the image detector as a two-dimensional image, a first read-out unit for reading the stored pixel data about a particular detector in a particular array, a second read-out unit for reading pixel data in the neighborhood of the pixel data read by the first read-out unit, a first arithmetic unit for measuring the magnitude of difference in sensitivity between the detector whose pixel data is read by the first read-out unit and the detector whose pixel data is read by the second read-out unit, and a second arithmetic unit for compensating for the deficiency of sensitivity on the basis of the output of the first arithmetic unit.

BACKGROUND OF THE INVENTION

The present invention relates to an image processing apparatus used inassociation with image detecting apparatus, such as X-ray imagedetecting apparatus, for medical and industrial use.

Latest type of X-ray image detecting apparatus are provided withone-dimensional sensor arrays each of which includes a plurality ofimage detectors of semiconductor. The sensor arrays are scannedperpendicular thereto so as to obtain a two-dimensional image. Inaddition, a Memory is provided for storing the two-dimensional image byarranging pixel data output by the image detectors in a predeterminedpattern.

This type of image detecting apparatus has a problem in that if anysensor array includes a defective image detector having a reducedsensitivity, the image produced by the defective detector is spoiled bya line noise.

If the defective image detector amounts to be more than one, oralternatively, if the extent of unequal sensitivity depends upontemperature, it is difficult to adjust all the image detectors so as tohave equal sensitivity.

SUMMARY OF THE INVENTION

The present invention is to provide an image processing apparatus usablein association with image detecting apparatus in order to remove a linenoise likely to occur because of unequal sensitivity between imagedetectors which constitute sensor arrays.

According to the present invention, the image processing apparatusincludes an image memory for storing pixel data output by the imagedetector as a two-dimensional image, a first read-out means for readingthe stored pixel data about a particular detector in a particular array,a second read-out means for reading pixel data in the neighborhood ofthe pixel data read by the first read-out means, a first arithmeticmeans for measuring the magnitude of difference in sensitivity betweenthe detector whose pixel data is read by the first read-out means andthe detector whose pixel date is read by the second read-out means, anda second arithmetic means for compensating for the deficiency ofsensitivity on the basis of the output of the first arithmetic means.

Pixel data output by the image detectors is linearly arranged and storedin the memory, and the first read-out means reads the pixel data whollyor partially from the memory. Then the second read-out memory readsanother pixel data in the neighborhood of the first-mentioned pixel dataread by the first read-out means. The first arithmetic means measuresthe magnitude of a difference in the sensitivity between a particularimage detector and the other image detectors.

If all the image detectors have a uniform sensitivity, and the resultingimage is sufficiently even with no dark or bright spots, the mean valueper pixel obtained from all the pixel data output by the particularimage detector must be in agreement with that obtained from all thepixel data output by the other image detectors in the neighborhood ofthe particular image detector. This means that the difference insensitivity is 0 (zero). If there is a difference between both the meanvalues, the difference indicates that there is a difference insensitivity. By using this difference, the second arithmetic meanscompensates for the deficient pixel data output by the particulardetector on the basis of the output by the first arithmetic means. Inthis way, according to the present invention, a line noise can beremoved with the original resolution of image maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram diagrammatically showing the entire structureof the image processing apparatus embodying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The exemplary apparatus 1 is provided with m rows of sensor arrays eacharray having n pieces of image detectors, which will hereinafter bereferred to merely as "detector". The sensor arrays are scannedperpendicular thereto so as to obtain a two-dimensional image whichconsists of (n×m) pieces of pixels. Now, suppose that the (i)th detectori outputs pixel data V_(ij) (j=1 to m), a mean value per pixel obtainedwill be: ##EQU1##

If all the detectors have equal sensitivity and the resulting image issafe from any noise, the value S_(i) ought to be equal to the mean valueS'_(i) obtained about a pixel situated near to the detector i.

If the detector i has a low sensitivity, the mean values will be asfollows:

    S.sub.i <S'.sub.i

This unequal relationship will be visually observed as a dark line(alternatively, an excessively bright line) formed by the outputs fromthe detector i. In order to remove this line noise, the difference Δbetween S_(i) and S'_(i) should be added to the data V_(ij) (j=1 to m).The exemplary apparatus 1 shown in FIG. 1 is based on this principle.

The exemplary apparatus 1 includes two memories 2 and 11, a firstcounter 3 and a second counter 4, data buses 5, 6, 7, and 20, a firstarithmetic unit 8, a second arithmetic unit 9, and a third arithmeticunit 10.

The memory 2 stores an image which consists of (n×m) pieces of pixelsobtained by scanning sensor arrays (not shown) each having n pieces ofdetectors. The first counter 3 indicates the position of pixel along thearray to which it belongs, and the second counter 4 indicates theposition of pixels in the scanning direction of the arrays.

The data buses 5, 6, and 7 are led from the memory 2. The data bus 5outputs data V_(ij) from the counters 3 and 4, and the data buses 6 and7 output data about pixel h, that is, (V.sub.(i-h)j ˜V.sub.(i-l)j) and(V.sub.(i+l)j ˜V.sub.(i+h)j). The data bus 20 is also connected to thememory 2 so as to change the pixel data V_(ij) about the positions ofpixels indicated by the counters 3 and 4 therethrough.

The arithmetic units 8 and 9 receive inputs delivered thereto throughthe data buses 6 and 7, respectively. The third arithmetic unit 10receives outputs from the arithmetic units 8 and 9, and the pixel dataV_(ij) through the data bus 5.

The arithmetic units 8 and 9 calculate a median (alternatively, a meanvalue) of data about the pixel h input thereto, and generate outputsl_(mj) and r_(mj), respectively.

The third arithmetic unit 10 houses four resistors l, r, c, and k(neither shown), and if the value |l_(mj) -r_(mj) | smaller than apredetermined value ε, the resistor l increases its value by l_(mj).Likewise, the resistor r increases its value by r_(mi), the resistor cincreases its value by V_(ij), and the resistor k increases its valueby 1. These increments are made for j (=1 to m). When j becomes equal tom, the third arithmetic unit 10 calculate the value Δ_(i) =(l+r)/2-c!/k. The resulting value Δ_(i) is stored in the (i)th of thememory 11 as a compensating value. When j becomes equal to 1, eachresistor in the third arithmetic unit 10 is reset to 0 (zero), andthereafter, the increment is performed.

In the above-mentioned process, the data 1 |l_(mj) -r_(mj) |>ε isignored. A large difference in sensitivity between adjacent pointsindicates that an image obtained is about an out-of-focus condition ofthe edge portion of the object. From this, the out-of-focus can berealized and remedied. The value ε, which is a parameter obtainablethrough experiments, is determined according to the magnitude to which aline noise due to different sensitivities between the detectors isremoved.

When the compensating value Δ_(i) for each detector is calculated, thecounters 3 and 4 are reset to their initial values, and the value(V_(ij) +Δ_(i)) is calculated by the calculator 12 while the value j ofthe second counter 4 is increased for the value i of each first counter3. The resulting value is put into a predetermined place in the memory 2through the data bus 20.

If a detector i in a particular array has a different sensitivity fromthat of the others, the magnitude of the difference can be expressed asa difference Δ_(i) between the mean value of all the pixel data outputby the faulty detector i and the mean value of all the pixel data outputby a detector in the neighborhood of the faulty detector i. By addingthis difference Δ_(i) to the pixel data V_(ij), that is, V_(ij) +Δ_(i),the deficient sensitivity can be easily compensated.

In the illustrated embodiment the compensating value for the detector iis obtained on the basis of (l+r)/2-c!/k and each pixel is compensatedby adding the difference Δ_(i) to the faulty value V_(ij) (j=1 to m).The compensation is not limited to this method but it is also possibleto use the following formula as a compensating value:

    where Δi=(l+r)/(2c).

What is claimed is:
 1. An apparatus for processing a two-dimensionalimage obtained by scanning sensor arrays of image detectorsperpendicular thereto, the apparatus comprising:an image memory forstoring pixel data output by the image detector as a two-dimensionalimage; a first read-out means for reading the stored pixel data about aparticular detector in a particular array; a second read-out means forreading pixel data in the neighborhood of the pixel data read by thefirst read-out means; a comparing arithmetic means for measuring themagnitude of difference in sensitivity between the detector whose pixeldata is read by the first read-out means and the detector whose pixeldata is read by the second read-out means; and a calculating arithmeticmeans for compensating for the deficiency of sensitivity on a basis ofthe output of the comparing arithmetic means, wherein the secondread-out means comprises a pair of data buses through which data aboutadjacent pixels located on each side of the pixel whose data is read bythe first read-out means, and wherein the apparatus further comprises afirst median arithmetic means and a second median arithmetic meanscoupled to said image memory and said comparing arithmetic means, saidfirst and second median arithmetic means for calculating a median or amean value of data about the pixels read by the data buses, and forgenerating outputs corresponding to the calculated median or mean valueto the comparing arithmetic means.
 2. An apparatus for processing atwo-dimensional image obtained by scanning sensor arrays of imagedetectors perpendicular thereto, the apparatus comprising:an imagememory for storing pixel data output by the image detector as atwo-dimensional image: a first read-out means for reading the storedpixel data about a particular detector in a particular array; a secondread-out means for reading pixel data in the neighborhood of the pixeldata read by the first read-out means; a comparing arithmetic means formeasuring the magnitude of difference in sensitivity between thedetector whose pixel data is read by the first read-out means and thedetector whose pixel data is read by the second read-out means; acalculating arithmetic means for compensating for the deficiency ofsensitivity on a basis of the output of the comparing arithmetic means;and a first counter and a second counter both connected to the imagememory, wherein the first counter indicates the position of the pixelsalong the array to which they belong and the second counter indicatesthe position of the pixels in a direction in which the arrays arescanned, wherein the second read-out means comprises a pair of databuses through which data about adjacent pixels located on each side ofthe pixel whose data is read by the first read-out means, and whereinthe apparatus further comprises a first median arithmetic means and asecond median arithmetic means coupled to said image memory and saidcomparing arithmetic means, said first and second median arithmeticmeans for calculating a median or a mean value of data about the pixelsread by the data buses, and for generating outputs corresponding to thecalculated median or mean value to the comparing arithmetic means. 3.The apparatus according to claim 2, wherein the comparing arithmeticmeans comprises a first resistor, a second resistor, a third resistor,and a fourth resistor arranged in such a manner that if the absolutevalue of a difference between the medians or mean values is below areference value, the first resistor is caused to increase its value bythe median or mean value output by the first median arithmetic means,the second resistor is caused to increase its value by the median ormean value output by the second median arithmetic means, the thirdresistor is caused to increase its value by the pixel data read by thefirst read-out means, and the fourth resistor is caused to increase itsvalue by 1 (one).